This project seeks to explore the functional organization of multiple representations in the auditory cortex of macaque monkeys. We are analyzing single unit responses to auditory stimuli in different auditory fields. In addition to pure tones, we are particularly testing various standardized complex sounds as stimuli. Neurons in the rostralarea (R) respond preferentially to low-frequency sounds, whereas neurons in the caudo-medial area (CM) prefer high frequencies. A combination of lesioning and tracer injections into matched frequency representations had revealed different inputs from the medial geniculate nucleus (MGN) of thalamus into areas R and CM, with CM depending more on input from AI for its responsiveness. In the lateral belt, which receives input from R and from primary auditory cortex (AI), most neurons do not respond well to pure tones. Instead, units in this region can be driven briskly by bandpass-filtered noise (BPN) pulses. Using this new type of stimulus, cochleotopic maps can be revealed along the antero-posterior axis in three lateral areas, which we have termed AL, ML, and CL. Neurons are tuned to the center frequency of the BPN bursts. They are also tuned to a best bandwidth of these stimuli, which is represented orthogonally to best center frequency, i.e. along the medio-lateral axis. Neurons in the lateral areas also respond well to frequency-modulated (FM) sounds and show selectivity for the rate and direction of FM stimuli. Noisy pulses and FM sounds are essential components of many species-specific communication calls, and neurons in the lateral belt areas often respond selectively to such calls as well. Filtering the communication sounds in specific ways reveals the existence of combination-sensitivity as described previously in the bat's auditory cortex. The lateral areas may thus constitute a further stepping stone in evolution towards the analysis of auditory patterns, in particular those relevant for communication, including human speech.